The invention relates to a fuel feed circuit for an aeroengine, and more particularly to a circuit that delivers fuel for feeding combustion chamber injectors of the engine and also for use as a hydraulic fluid for controlling actuators of variable-geometry members of the engine.
Usually, a fuel feed circuit of an aeroengine has a pump system made up of a low-pressure pump associated with a high-pressure pump. The high-pressure pump is generally in the form of a positive displacement gear pump of constant cylinder capacity that is driven by the engine via an accessory gearbox (AGB). The function of the pump is to deliver fuel at high pressure to the combustion chamber injectors and to the actuators of the variable-geometry members of the engine.
Nevertheless, the rate at which fuel is delivered is not matched to the real needs of the engine for all of its operating points, and it exceeds those needs over a wide range of speeds of rotation of the engine. The flow of fuel that is not consumed by the fuel circuit during those speeds of rotation of the engine is therefore returned upstream from the high-pressure pump. This return leads to an increase in the temperature of the fuel and takes mechanical power from the pump that does not contribute to thrust from the engine.
In order to remedy this problem, it is known to have recourse to two-stage high-pressure pumps, i.e. pumps presenting two stages of gears that are driven simultaneously by the engine and that have different cylinder capacities. With that type of architecture, the high-pressure pump preferably operates using a single stage when the engine operating point does not require a large cylinder capacity. Under such circumstances, the flow from the other pump is returned in full while conserving low-pressure loading, thereby diminishing the amount of mechanical power that is drawn from this stage. For engine operating points that require a greater cylinder capacity, the second pump is activated.
Document U.S. Pat. No. 7,234,293 discloses an example of a two-stage high-pressure pump. In particular, that document describes a system for switching between the one- and two-stage configurations on the basis of a modification to the regulator valve that has two return sections (one for each stage of the high-pressure pump).    Unfortunately, that type of switching gives rise to disturbances in the metered flow rate of the fuel, which disturbances are particularly harmful in terms of the accuracy with which the fuel is metered.